Effect of antiplasticization on gas sorption and transport. I. Polysulfone

The addition of tricresyl phosphate, N-phenyl-2-naphthylamine, and 4,4′-dichlorodiphenyl sulfone to polysulfone causes changes in thermal and mechanical properties of the glassy mixtures associated with antiplasticization, i.e., reduction in glass transition temperature and increase in stiffness. These changes are also found to be accompanied by reductions in sorption of carbon dioxide and the permeability coefficients for helium, carbon dioxide, and methane at low diluent concentrations with reversal of these trends at higher levels as also occurs for the mechanical properties. Detailed analyses of data for carbon dioxide are given in terms of the dual sorption and mobility models often used for glassy polymers. The mobility for gas transport was found to decrease with diluent addition. The major cause for the decreased sorption is the reduction in glass transition temperature accompanying addition of the diluents. The changes in transport behavior approximately parallel the changes in mechanical behavior. These trends are not even qualitatively correlated with estimates of the excess volume changes associated with addition of the diluents to polysulfone.     

Sorptive dilation of poly(vinyl benzoate) and poly(vinyl butyral) by carbon dioxide

Dilation of poly(vinyl benzoate) and poly(vinyl butyral) accompanying sorption of carbon dioxide is measured with a cathetometer under pressures up to 50 atm at 25°C. Sorption isotherms for carbon dioxide in these polymers were also determined gravimetrically. Each dilation isotherm plotted versus pressure, as well as the sorption isotherm, showed an inflection point corresponding to the glass transition of the polymer-gas system. The dilation isotherms changed their form at that point from concave to convex to the pressure axis or to a straight line. Dilation and sorption isotherms exhibited time-dependent hysteresis below the inflection point but not above the point. Partial molar volumes of carbon dioxide in polymers, which were determined from dilation and sorption data above the point, were found to be independent of concentration and larger than those below the point. The latter volumes depended on concentration. Based upon the extended dual-mode sorption concept, which takes account of plasticization of polymer by sorbed gas, a dilation model was developed. Dilation data were described well by the model.     

The effect of lattice compressibility on the thermodynamics of gas sorption in polymers

A compressible lattice model with holes, the glassy polymer lattice sorption model (GPLSM), was used to model the sorption of carbon dioxide, methane, and ethylene in glassy polycarbonate and carbon dioxide in glassy tetramethyl polycarbonate. For glassy polymers, an incompressible lattice model, such as the Flory–Huggins theory, requires concentration-dependent and physically unrealistic values for the lattice site volumes in order to satisfy lattice incompressibility. Rather than forcing lattice incompressibility, GPLSM was used and reasonable parameter values were obtained. The effect of conditioning on gas sorption in glassy polymers was analyzed quantitatively with GPLSM. The Henry's law constant decreases significantly upon gas conditioning, reflecting changes in the polymer matrix at infinite dilution. Treating the Henry's law constant as a hypothetical vapor pressure at infinite dilution, gas molecules in the conditioned polymer are less “volatile” than those in the unconditioned polymer. Flory–Huggins theory was used to model the sorption of carbon dioxide, methane, and ethylene in silicone rubber. Above the glass transition temperature, the criterion of lattice incompressibility for Flory-Huggins theory was satisfied with physically realistic and constant values for the lattice site volumes. © 1992 John Wiley & Sons, Inc.     

Dual-mode free volume model for diffusion of gas molecules in glassy polymers

The development of a new model for the diffusion of gas molecules in glassy polymers is presented which utilizes concepts from free volume theory and relies on a dual-mode interpretation of sorptive dilation in glassy polymers. Three assumptions are made in the development of the model. First, the free volume available for molecular transport processes is taken as constant below the glass transition temperature. Second, two populations of gas molecules are assumed to exist—one which contributes to the maintenance of an iso-free volume state upon sorptive dilation and one which does not contribute owing to sorption into regions of unrelaxed volume. Third, the former population is assumed to be mobile while the latter is not. The resulting model predicts, at constant temperature, a diffusion coefficient that is independent of solute volume fraction. This is in contrast to the widely used dual-mode sorption model with partial immobilization for gas transport in glassy polymers which leads to a diffusion coefficient that is dependent on solute mole fraction through the molar gas concentration. The new model is used to interpret gas transport data from permeation experiments for carbon dioxide, methane, and ethylene in three polycarbonates. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1737–1746, 1997     

Sorptive dilation of polysulfone and poly(ethylene terephthalate) films by high-pressure carbon dioxide

Dilation of polysulfone (PSUL) and crystalline poly(ethylene terephthalate) (PET) films accompanying sorption of carbon dioxide is measured by a cathetometer under high pressure up to 50 atm over the temperature range of 35–65°C. Sorptive dilation isotherms of PSUL are concave and convex to the pressure and concentration axes, respectively, and both isotherms exhibit hysteresis. Each dilation isotherm plotted versus pressure and concentration for the CO₂-PET system shows an inflection point, i.e., a glass transition point, at which the isotherm changes from a nonlinear curve to a straight line. Dilation isotherms of PET below the glass transition point are similar to those of the CO₂-PSUL system, whereas the isotherms above the glass transition point are linear and exhibit no hysteresis. Partial molar volumes of CO₂ in these polymers are determined from data of sorptive dilation. On the basis of the extended dual-mode sorption model and the current data, primitive equations for gas-sorptive dilation of glassy polymers are proposed.     

Sorption and dilation in poly(ethyl methacrylate)–carbon dioxide system

Sorption and dilation in the system poly(ethyl methacrylate) (PEMA) and carbon dioxide are reported for pressures up to 50 atm over the temperature range 15–85°C. The sorption isotherms were obtained gravimetrically. The dilation accompanying sorption was measured directly with a cathetometer. At low temperatures the sorption and dilation isotherms were concave toward the pressure axis in the low-pressure region and turned to convex with increasing pressure. As the experimental temperature approached and exceeded the glass transition temperature of 61°C, both isotherms became convex or linear over the whole range of pressure. Partial molar volumes of CO₂ in PEMA were obtained from sorption and dilation data, which were described well by the extended dual-mode sorption and dilation models developed recently. The temperature dependence of the dual-mode parameters and the isothermal glass transition are discussed.     

Sulfone-Containing polymers as high barrier materials

Three types of sulfone-containing polymers, poly(carbonate-sulfone)s, poly(ester-sulfone)s, and poly(urethane-sulfone)s, were characterized as high barrier materials. They were made by condensing sulfone-containing diol, 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333), or 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343), with diphenyl carbonate, diphenyl esters, and diisocyanates, respectively. The incorporation of polar sulfone groups into polymer backbones increases the glass transition temperature of polymers in all cases; however, the increment is different with different functional linkages. The increments in polycarbonates and polyesters are higher than that in polyurethanes. This is because the interactions between carbonate or ester groups are much weaker than the interactions between sulfone groups, whereas the hydrogen bonding between urethane groups is comparable with the polar interaction between sulfone groups. The polymers were coated on 50-μm-thick Kapton films by solution casting and their permeabilities toward carbon dioxide were measured at 25°C using the ASTM D1434 volumetric method. The sulfone-containing polymers have carbon dioxide permeability coefficients at least 50 times smaller than the corresponding polymers without sulfone groups. The carbon dioxide barrier properties of sulfone-containing polymers are comparable with ethylene/vinyl alcohol copolymers (EVAL), which are commercial high barrier polymers. An isomer effect on polymer permeability was observed in the aromatic-aliphatic poly(ester-sulfone) series. The permeability coefficients of the aromatic-aliphatic poly(ester-sulfone)s decrease from terephthalate to isophthalate to phthalate, corresponding to the increase of chain flexibility above the T_g. These results support the hypothesis that high chain flexibility in the rubbery state and a glass transition temperature above room temperature are two key factors that promote low permeability. © 1994 John Wiley & Sons, Inc.     

Gas sorption and diffusion processes in polymer matrices at high pressures

A theoretical approach has been developed to describe the processes of gases diffusion and sorption in rubbery and glassy polymers. Various models (Flory-Huggins, dual-mode sorption, gas-polymer-matrix) used for interpreting the sorption-diffusion experiments are discussed within this approach framework. Experimental data on carbon dioxide sorption in glassy and rubbery polymers have been considered using the proposed approach. The comparison of the experimental and theoretical data has permitted to make the conclusion on the developed concepts adequacy. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1339–1348, 1997     

Analysis of gas sorption in glassy polymers with the GAB model: An alternative to the dual mode sorption model

The suitability of the Guggenheim–Anderson–De Boer (GAB) model for the parameterization of gas sorption isotherms and their dependences on temperature is explored. The GAB model implies that molecules adsorb on inner surfaces of the polymer in multilayers, which contrasts with the assumptions of the classical Dual Mode Sorption (DMS) model which implies the simultaneous occurrence of Henry‐like dissolution and Langmuir's case I adsorption. The GAB model shows similar efficacy of the parameterization of the gas sorption isotherms in polymers as the DMS model. The isosteric heat of adsorption shows clear dependence on relative surface coverage for carbon dioxide sorption in cellulose acetate, polyethylene terephthalate, and the first polymer of intrinsic microporosity (PIM‐1), thus allowing for the occurrence of adsorption multilayers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1490–1495     

CO2 sorption and transport in miscible poly(phenylene oxide)/polystyrene blends

The sorption and permeation of carbon dioxide gas in miscible blends of poly(phenylene oxide) and polystyrene was measured as a function of pressure at 35°C over the entire range of blend compositions. The results are well described quantitatively by the dual sorption and dual mobility models developed for glassy polymers. The Henry's law sorption parameter was analyzed by the Flory—Huggins theory of ternary mixtures to obtain an interaction parameter which quantifies the exothermic heat of mixing for this blend system. The Langmuir capacity term was successfully related to the unrelaxed volume of the glassy blends. Transport properties of the blends were found to lie well below predictions based on simple additivity which is consistent with the strong interaction between the two polymers.     

Swelling of Polyheteroarylenes in Supercritical Carbon Dioxide

Two series of polyheteroarylenes have been investigated with regard to their physical properties before and after swelling with supercritical carbon dioxide. The study of the dependence of glass transition temperature and free volume of polymers on their conformational rigidity showed that the process of swelling in supercritical carbon dioxide is influenced by the voluminous side groups and by the high boiling solvent N-methylpyrolidinone used for the preparation of the polymers which facilitates the formation of crosslinks or complexes with the macromolecular chains.     

Characterization of the motion of spin probes and spin labels in amorphous polymers with two-dimensional field-step ELDOR

The motion of nitroxide spin probes and spin labels in amorphous polymers is studied below the glass transition temperature with a two-dimensional pulsed electron double-resonance experiment. Polystyrene and a liquid crystalline side group polymer are studied using both spin probes and spin labels covalently bound to specific sites along the polymer chain. Two methyl acrylic polymers differing only in their side group structure and polyvinylacetate are compared and large differences in the molecular dynamics deduced from both the nuclear and the electron spin relaxation rates are observed as the glass transition is approached. The results demonstrate the complexity of small amplitude motion in simple polymers below the glass transition temperature and show that it is very sensitive to the packing in the polymer. © 1996 John Wiley & Sons, Inc.     

Transport properties of small molecules in zwitterionic polymers

Despite great interests in using zwitterionic polymers for membrane surface modification to enhance antifouling properties, there lacks fundamental understanding of the relationship between polymer structure and water/salt separation properties. In this study, two series of zwitterionic polymers were prepared from sulfobetaine methacrylate and 2‐methacryloyloxyethyl phosphorylcholine. Both are crosslinked by poly(ethylene glycol) diacrylate (PEGDA). These copolymers were thoroughly characterized in terms of sol‐gel fraction, density, glass transition temperature, contact angle, water and salt transport properties, and pure‐gas permeability. Interestingly, the zwitterionic polymers exhibit water sorption and permeability similar to noncharged poly(ethylene glycol)‐based materials. These zwitterionic polymers exhibit lower NaCl diffusivity and permeability and thus higher water/NaCl selectivity than the non‐charged PEG‐based materials at similar water volume fractions, demonstrating their promise for membrane surface modification for desalination and wastewater treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1924–1934     

The transport of gases in synthetic polymeric membranes — an historic perspective

The early history of gas transport studies is briefly reviewed. These studies were almost entirely concerned with natural rubber membranes. By 1880 the simple form of the solution-diffusion model had been derived and checked and by 1920 the time lag method for determining diffusion coefficients had been developed. The work which followed, for the next thirty years, was mainly concerned with natural and synthetic elastomers all well above their glass transition temperature, mainly hydrocarbon in nature, and non-crystalline. p]A number of reasonably successful correlations were shown between the gas transport parameters and the physical and chemical properties of the polymers. It is clear now that these correlations break down with the polar polymers. p]Functional relationships which have stood the test of time are those between the force parameters of the gas and the logarithms of the solubility coefficients. The linear relationship between the pre-exponential factors (or the entropies) of the diffusion coefficients and the activation energies also holds for most polymers. The remarkable constancy of the ratios of the permeability coefficients for the atmospheric gases through a large number of different polymers also has continued to be valid. p]The arrival of numerous new polymers introduced the dual complications of crystallinity (and morphology) and the glassy state. The concept of dual mode sorption cast doubt on many of the results and conclusions reached with glassy polymers. Recent work, however, shows great promise that these difficulties can be overcome and attention can again be focused on the mechanism of such transport. Finally, the behavior of the gas transport parameters above and below the glass transition temperatures is discussed.     

Mechanism of diffusion and sorption of carbon dioxide in poly(vinyl acetate) above and below the glass transition temperature

The pressure dependence below 1 atm of the apparent diffusion and permeation coefficients were observed by using the permeation time lag method for carbon dioxide in poly(vinyl acetate), which has a glass transition near room temperature, at temperatures ranging from 8 to 50°C. Above the glass transition temperature, pressure dependence of the diffusion and permeation coefficient has not been observed; hence, Fick's law with a concentration independent diffusion coefficient applies. On the other hand, in the glassy state, the apparent diffusion coefficient shows pressure dependence. Moreover, the behavior of the pressure dependence does not show a clear curve in the ranges between 30°C to 17°C. Above 17°C, the apparent diffusion coefficients show discontinuities, but below 17°C increase with pressure is regular. Using the theoretical prediction of Paul, a computer was used in the numerical calculation to determine the true diffusion coefficient and other dual sorption parameters. p]The compensated diffusion coefficients controlled only by Henry's law dissolution was described by three straight lines with two intersection in the form of Arrhenius plots, which give good agreement with both our results for He and Ar and those of Meares. It is assumed that beside the dual sorption mechanism, another effect, for instance some relaxation effect may also contribute to the diffusion for carbon dioxide in poly(vinyl acetate) near the glass transition temperature region.     

Temperature dependence of ESR spectra of nitroxide spin probe in glassy polymers

Temperature dependencies of ESR spectra of nitroxide spin probes in glassy polymers near and below glass transition temperature were examined in detail. Three temperature ranges, each characterized by specific changes in spectral shape, were defined. (i) In the low temperature range, ESR spectra of nitroxide radical in glassy polymer matrix weakly depend on temperature and remain qualitatively the same. (ii) In the intermediate temperature range, significant changes in the shape of spectra are observed. (iii) A new phenomenon was revealed near and below glass transition temperature: narrowing of linewidths occurs while the ratio of amplitudes of different components varies insignificantly. Analysis of molecular rotational mobility was carried out by means of commonly used empirical approaches. It was shown that widely used formulas and empirical approaches are not applicable for characterization of molecular mobility in glassy polymers. Mechanisms of rotational molecular movements in glassy polymers are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 563–575, 2009     

Gas solubility of carbon dioxide in poly(lactic acid) at high pressures: Thermal treatment effect

The sorption of carbon dioxide in glassy Poly(lactic acid) (PLA) films was studied by quartz crystal microbalance (QCM) at high pressures. Two thermal treatments, melted and quenched, were performed in PLA with two different L:D contents, 80:20 and 98:2, films and compared with a third thermal protocol, annealed, and used in a previous work. The results obtained show that for pressures higher than 2 MPa, the carbon dioxide solubility is larger in PLA 80:20 than in PLA 98:2, indicating that the L:D plays a dominant role on this property. The thermal treatments only affect the gas solubility in PLA 98:2. Sorption isotherms at temperatures 303, 313, and 323 K, below the glass transition temperature of the polymer, and pressures up to 5 MPa were measured and analyzed with three different models, the dual‐mode sorption model, the Flory–Huggins equation, and a modified dual‐mode sorption model where the Henry's law term was substituted by the Flory–Huggins equation. This last model performs especially well for CO₂ in PLA 80:20, due to the convex upward curvature of the solubility isotherms for that system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 616–625, 2007     

Glassy polymer‐sorption phenomena measured with a quartz crystal microbalance technique

The quartz crystal microbalance (QCM) method is applied to the measurement of CO₂ sorption in glassy poly(ethylene terephthalate) (PET), poly(methyl methacrylate), and polysulfone. Polymer thin films in the thickness range of 350–550 nm are prepared by spin‐casting onto the quartz crystal devices. Sorption isotherms at temperatures below the glass transition are analyzed with the dual‐mode sorption model. As‐cast, quenched, and slow‐cooled thermal‐conditioning protocols yield consistent trends in the sorption level, namely, as‐cast > quenched > slow‐cooled. The sorption levels and model results for the quenched‐conditioned samples measured with QCM compare favorably with those reported from the pressure‐decay and gravimetric methods on thick films. With extended analysis of PET, the QCM technique is also useful for the exploration of the temperature dependence associated with gas sorption in glassy polymer systems. Measured heats of sorption and the collapse of the Langmuir component near the PET glass‐transition temperature agree with those reported previously. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2109–2118, 2003     

Carbon dioxide, ethylene and water vapor sorption in poly(lactic acid)

The objective of this work is to study the gas/vapor sorption in poly(lactic acid) (PLA) with a 98:2 (l:d) ratio using a quartz crystal microbalance (QCM). For that purpose, the sorption of carbon dioxide, ethylene and water vapor in poly(lactic acid) (PLA) with a 98:2 (l:d) ratio, in temperature range from 283 to 313 K and up to atmospheric pressure was measured. The measured isotherms indicate that the sorption mechanism is sorbate dependent, since carbon dioxide and ethylene seem to have predominantly a Langmuir type of mechanism while water is predominantly Henry controlled. Two temperature protocols were used and only ethylene sorption is affected by them. Comparisons with previously measured gas sorption data in PLA 80:20 using the same temperature protocol indicate that the l:d ratio plays a dominant role in gas/vapor sorption in PLA.     

“Second component” effects in sorption and permeation of gases in glassy polymers

Data for CO² permeability through Kapton polyimide at 60°C are reported for upstream pressures up to 240 psia (16.33 atm) in the presence and absence of water vapor in the feed. The carbon dioxide flux was depressed by the presence of the water vapor. This phenomenon is analyzed in terms of the dual mode sorption and transport models. Together with other recent sorption and permeation data, this study suggests that competition of mixed penetrants for sorption sites and transport pathways associated with unrelaxed volume in glassy polymers is a general feature of gas/glassy polymer systems. The permselectivity of a membrane to a mixture of penetrants is strongly related to its ability to maintain a size and shape differentiating matrix, that is, to remain essentially unplasticized under operating conditions. Under such conditions, competition among penetrants for excess volume will be a generally important consideration for modeling gas permeation in permselective membranes.